Anti-Rotation Fixation Element for Spinal Prostheses

ABSTRACT

Prostheses, systems, and methods are provided for replacement of natural facet joints between adjacent vertebrae with vertebral prostheses. A portion of the vertebral prosthesis includes anti-rotation and/or anti-pullout elements to prevent or reduce prosthesis fastener rotation or pull out as a result of torques applied to the prosthesis. Various tools and methods aid the process of surgically adding the vertebral prosthesis to a patient&#39;s vertebra.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation application claiming priorityto U.S. patent application Ser. No. 10/831,657, filed on Apr. 22, 2004,the entire contents of which are incorporated by reference.

FIELD OF THE INVENTION

This invention relates to prostheses, systems, and methods for treatingvarious types of spinal pathologies, and in particular relates toattachment of prostheses to spinal vertebrae.

BACKGROUND OF THE INVENTION

The human spinal column 10, as shown in FIG. 1, is comprised of a seriesof thirty-three stacked vertebrae 12 divided into five regions. Thecervical region includes seven vertebrae, known as C1-C7. The thoracicregion includes twelve vertebrae, known as T1-T12. The lumbar regioncontains five vertebrae, known as L1-L5. The sacral region is comprisedof five vertebrae, known as S1-S5, while the coccygeal region containsfour vertebrae, known as Co1-Co4.

FIG. 2 depicts a superior plan view of a normal human lumbar vertebra12. Although human lumbar vertebrae vary somewhat according to location,they share many common features. Each vertebra 12 includes a vertebralbody 14. Two short bones, the pedicles 16, extend backward from eachside of the vertebral body 14 to form a vertebral arch 18.

At the posterior end of each pedicle 16, the vertebral arch 18 flaresout into broad plates of bone known as the laminae 20. The laminae 20fuse with each other to form a spinous process 22. The spinous process22 serves for muscle and ligamentous attachment. A smooth transitionfrom the pedicles 16 to the laminae 20 is interrupted by the formationof a series of processes.

Two transverse processes 24 thrust out laterally on each side from thejunction of the pedicle 16 with the lamina 20. The transverse processes24 serve as levers for the attachment of muscles to the vertebrae 12.Four articular processes, two superior 26 and two inferior 28, also risefrom the junctions of the pedicles 16 and the laminae 20. The superiorarticular processes 26 are sharp oval plates of bone rising upward oneach side of the vertebrae, while the inferior processes 28 are ovalplates of bone that jut downward on each side.

The superior and inferior articular processes 26 and 28 each have anatural bony structure known as a facet. The superior articular facet 30faces upward, while the inferior articular facet 31 (see FIG. 3) facesdownward. When adjacent vertebrae 12 are aligned, the facets 30 and 31,capped with a smooth articular cartilage, interlock to form a facetjoint 32, also known as a zygapophyseal joint.

The facet joint 32 is composed of a superior half and an inferior half.The superior half is formed by the vertebral level below the joint 32,and the inferior half is formed by the vertebral level above the joint32. For example, in the L4-L5 facet joint, the superior half of thejoint 32 is formed by bony structure on the L5 vertebra (i.e., asuperior articular surface and supporting bone 26 on the L5 vertebra),and the inferior half of the joint 32 is formed by bony structure on theL4 vertebra (i.e., an inferior articular surface and supporting bone 28on the L4 vertebra).

An intervertebral disc 34 between each adjacent vertebrae 12 permitsgliding movement between the vertebrae 12. The structure and alignmentof the vertebrae 12 thus permit a range of movement of the vertebrae 12relative to each other.

Back pain, particularly in the “small of the back” or lumbosacral(L4-S1) region, is a common ailment. In many cases, the pain severelylimits a person's functional ability and quality of life. Such pain canresult from a variety of spinal pathologies.

Through disease or injury, the laminae, spinous process, articularprocesses, or facets of one or more vertebral bodies can become damaged,such that the vertebrae no longer articulate or properly align with eachother. This can result in an undesired anatomy, loss of mobility, andpain or discomfort.

For example, the vertebral facet joints can be damaged by eithertraumatic injury or by various disease processes. These diseaseprocesses include osteoarthritis, ankylosing spondylolysis, anddegenerative spondylolisthesis. The damage to the facet joints oftenresults in pressure on nerves, also called “pinched” nerves, or nervecompression or impingement. The result is pain, misaligned anatomy, anda corresponding loss of mobility. Pressure on nerves can also occurwithout facet joint pathology, e.g., a herniated disc.

One type of conventional treatment of facet joint pathology is spinalstabilization, also known as intervertebral stabilization.Intervertebral stabilization prevents relative motion between thevertebrae. By preventing movement, pain can be reduced. Stabilizationcan be accomplished by various methods. One method of stabilization isspinal fusion. Another method of stabilization is fixation of any numberof vertebrae to stabilize and prevent movement of the vertebrae.

Another type of conventional treatment is decompressive laminectomy.This procedure involves excision of the laminae to relieve compressionof nerves.

These traditional treatments are subject to a variety of limitations andvarying success rates. None of the described treatments, however, putsthe spine in proper alignment or returns the spine to a desired anatomyor biomechanical functionality. In addition, stabilization techniqueshold the vertebrae in a fixed position thereby limiting a person'smobility.

Prostheses, systems, and methods exist which can maintain more spinalbiomechanical functionality than the above discussed methods and systemsand overcome many of the problems and disadvantages associated withtraditional treatments for spine pathologies. One example of suchprosthesis is shown in FIG. 4. FIG. 4 shows an artificial cephalad andcaudal facet joint prostheses 36 and 50 for replacing a natural facetjoint. Cephalad joint prosthesis 36 replaces the inferior half of anatural facet joint. Cephalad prosthesis 36 has a bearing element 38with a bearing surface 40. Caudal joint prosthesis 50 replaces thesuperior half of a natural facet joint. Caudal prosthesis 50 has abearing element 52 with a bearing surface 54. Conventional fixationelements 56 attach cephalad and caudal facet joint prostheses 36 and 50to a vertebra in an orientation and position that places bearing surface40 in approximately the same location as the natural facet joint surfacethe prosthesis replaces. The prosthesis may also be placed in a locationother than the natural facet joint location.

The spinal column permits the following types of movement: flexion,extension, lateral movement, circumduction and rotation. Each movementtype represents relative movement between adjacent vertebra or groups ofvertebrae. In addition, these relative movements may be simple movementsof a single type but it is more likely that a single movement of thespine may result in several movement types or compound movementoccurring contemporaneously. In the illustration of FIG. 4, thistranslates into movement between the upper vertebral body 12 attached tothe cephalad prosthesis 36 and the lower vertebral body 12 attached tocaudal prosthesis 50. The movement of the vertebral bodies 12 can resultin large, complex forces being generated and transmitted through theprosthesis. The point or points of contact between the bearing surface40 of the cephalad prosthesis 36 and the bearing surface 54 of thecaudal prosthesis 50 can transmit enormous amounts of force onto boththe cephalad and caudal facet joint prostheses 36 and 50. The distancebetween each conventional fixation element 56 and the point or points ofcontact serves as a lever arm, thereby applying an enormous amount ofaxial, lateral and torque forces about each of the conventional fixationelements 56, which act as fulcrums. Thus, cephalad prosthesis 36experiences a force somewhere on bearing surface 40, which is expressedas axial, lateral and torque forces about the conventional fixationelement 56 of the cephalad prosthesis 36; and likewise, caudalprosthesis 50 experiences a force somewhere on bearing surface 54, whichis expressed as axial, lateral and torque forces about the conventionalfixation element 56 of the caudal prosthesis 50. As a result, enormousamounts of such forces can be generated and must be absorbed by thefacet joint prostheses and its anchoring system(s).

The existence of enormous amounts of torque presents significantproblems for permanent fixation of facet joint prostheses into vertebra.Over time, this torque can act to loosen conventional fixation elements,ruin the facet joint, and require more surgical intervention to restorethe facet joint prostheses in the vertebra.

Thus, what is needed is a solution to the torque problem experienced byfacet joints of artificial vertebral prostheses.

SUMMARY OF THE INVENTION

The present invention provides prostheses, systems, and methods designedto replace natural facet joints and possibly part of the lamina atvirtually all spinal levels including L1-L2, L2-L3, L3-L4, L4-L5, L5-S1,T11-T12, and T12-L1, using attachment mechanisms for securing theprostheses to the vertebrae. The prostheses, systems, and methods helpestablish a desired anatomy to a spine and return a desired range ofmobility to an individual. The prostheses, systems, and methods alsohelp lessen or alleviate spinal pain by relieving the source nervecompression or impingement.

For the sake of description herein, the prostheses that embody featuresof the invention are identified as either “cephalad” or “caudal” withrelation to the portion of a given natural facet joint they replace. Aspreviously described, a natural facet joint, such as facet joint 32(FIG. 3), has a superior half and an inferior half. In anatomical terms,the superior half of the joint is formed by the vertebral level belowthe joint, which can thus be called the “caudal” portion of the facetjoint because it is closer to the feet of the person. The inferior halfof the facet joint is formed by the vertebral level above the joint,which can thus be called the “cephalad” portion of the facet jointbecause it is closer to the head of the person. Thus, a prosthesis that,in use, replaces the caudal portion of a natural facet joint (i.e., thesuperior half) will be called a “caudal” prosthesis. Likewise, aprosthesis that, in use, replaces the cephalad portion of a naturalfacet joint (i.e., the inferior half) will be called a “cephalad”prosthesis.

In one aspect, a vertebral prosthesis includes a first bearing elementand a first fixation element coupled to the first bearing element. Thefirst bearing element can be shaped to form a facet joint with a secondbearing element. The first fixation element can be inserted into a holein a vertebra.

The first fixation element can include an anti-rotation element. Theanti-rotation element can be coupled to at least a portion of thevertebra. This portion of the vertebra can define the hole in thevertebra. The anti-rotation element can be adapted to resist arotational force. With no resistance, the rotational force may causerotation of the first fixation element within the hole in the vertebra.

In some embodiments, the hole in the vertebra may be just one hole. Inother embodiments, there may be multiple holes in the vertebra. In thecase of multiple holes in the vertebra, the first fixation element canbe inserted into just one hole in the vertebra, or into multiple holesin the vertebra. Also in the case of multiple holes in the vertebra, therotation force may cause rotation of the first fixation element withinjust one hole in the vertebra, or within multiple holes in the vertebra.

In various embodiments, the second bearing element with which the firstbearing element forms a facet joint, can be part of a second prosthesis,or part of a natural vertebra. If the second bearing element is part ofa second prosthesis, the second prosthesis can be one of the embodimentsdiscussed herein, or another type of prosthesis.

The fixation element may be secured directly into the vertebral body, orcan be attached and/or “fixed” using a supplemental fixation materialsuch as bone cement, allograft tissue, autograft tissue, adhesives,osteo-conductive materials, osteo-inductive materials and/or bonescaffolding materials. In one embodiment, the first fixation element canbe enhanced with a bony in-growth surface, such as surfaces createdusing sintering processes or chemical etching (Tecomet Corporation ofWoburn, Mass.) which can help fix the fixation element within avertebra. The bony in-growth surface can cover a portion or all of thefirst fixation element.

A width of the prosthesis may be constant, or vary. For example, a widthof a proximal end of the first fixation element can exceed a width of adistal end of the first fixation element. A width of a proximal end ofthe anti-rotation element can exceed a width of a distal end of theanti-rotation element. In an alternate embodiment, a width of a distalend of the first fixation element can exceed a width of a proximal endof the first fixation element.

The anti-rotation element can be coupled to the vertebra by beingdirectly connected to the vertebra. The anti-rotation element also canbe coupled with at least cement to the vertebra.

In some embodiments, the anti-rotation element includes a wing. The wingcan be positioned at a proximal of distal portion of the first fixationelement. When the first fixation element is inserted into a first holeor holes in the vertebra, the wing can be inserted into a second hole ofthe vertebra.

In some embodiments, the anti-rotation element includes a blade. Theblade can be positioned at a proximal or distal portion of the firstfixation element. When the first fixation element is inserted into afirst hole or holes in the vertebra, the blade can also be inserted intothe first hole in the vertebra.

In some embodiments, the anti-rotation element includes a paddle. Thepaddles can be positioned at a distal or proximal portion of the firstfixation element. The first fixation element can be straight, or includeone or more bends. The anti-rotation element can include one or moregrooves positioned distally and/or proximally from the paddle. Theanti-rotation element can also include other features, such as one ormore wings positioned proximally or distally from the paddle, and/or oneor more blades positioned proximally or distally from the paddle.

In some embodiments, the anti-rotation element includes an intersectionof three or more projections. The intersection can be positioned at adistal or proximal portion of the first fixation element.

In some embodiments, the anti-rotation element includes a helicalprojection. The anti-rotation element can include an intersection of twoor more helical projections.

In some embodiments, the anti-rotation element includes a longitudinaldepression. The longitudinal depression can have a longitudinallyvarying profile. The longitudinal depressions can be a helicallongitudinal depression, a groove, or a flute. The longitudinaldepression can help define a spline. The anti-rotation element mayfurther include a perimeter (circumferential) depression. The perimeterdepression can be a perimeter undercut.

In some embodiments, the anti-rotation element can include separatedmembers. The first fixation element can include a longitudinal hole. Afilling element can be inserted into the longitudinal hole and spreadthe separated members of the anti-rotation element. The separatedmembers can be positioned at a distal portion of the first fixationelement.

In various embodiments, the anti-rotation element can define a hole,into which the first fixation element is inserted. Alternatively, thefirst fixation element can define a hole into which the anti-rotationelement is inserted. In various embodiments, the hole can be tapered(using, for example, a tapered broach) and/or the first fixation elementcan have a taper. The anti-rotation element can have a taper. Theanti-rotation element can be coupled to the first fixation element by aninterference fit. The anti-rotation element can include a bend, or bestraight. The first fixation element can be straight, or include a bend.

In some embodiments, the anti-rotation element includes one or moreproximal projections.

In another aspect, a vertebral prosthesis includes a first bearingelement and a first fixation element. The first bearing element can beshaped to form a facet joint with a second bearing element. The firstfixation element can be coupled to the first bearing element. The firstfixation element can be inserted into a hole in the vertebra. The firstfixation element can be shaped to resist a rotational force. With noresistance, the rotational force may cause rotation of the firstfixation element within the hole in the vertebra.

In various embodiments, the second bearing element with which the firstbearing element forms a facet joint, can be part of a second prosthesis,or part of a natural vertebra. If the second bearing element is part ofa second prosthesis, the second prosthesis can be one of the embodimentsdiscussed herein, or another type of prosthesis.

The first fixation element can be enhanced with a bony in-growthsurface, which can help fix the fixation element within a vertebra. Thebony in-growth surface can cover a portion or the entire first fixationelement.

A width of the prosthesis may be constant, or vary. For example, a widthof a proximal end of the first fixation element can exceed a width of adistal end of the first fixation element. A width of a proximal end ofthe anti-rotation element can exceed a width of a distal end of theanti-rotation element. In another embodiment, the width of a distal endof the anti-rotation element can exceed a width of a proximal end of theanti-rotation element.

The anti-rotation element can be coupled to the vertebra by beingdirectly connected to the vertebra. The anti-rotation element also canbe coupled with at least cement to the vertebra.

In some embodiments, the first fixation element can be shaped with abend. The first fixation element can have a taper.

In another aspect, a vertebral prosthesis method includes coupling afirst bearing element to a first fixation element, coupling ananti-rotation element to the first fixation element (as a feature of thecomponent or as a separate component), and inserting the first fixationelement into a hole in the vertebra. The first bearing element can beshaped to form a facet joint with a second bearing element. Theanti-rotation element can be adapted to resist a rotational force. Withno resistance, the rotational force may cause rotation of the firstfixation element within the hole in the vertebra.

In another aspect, a vertebral prosthesis preparation method includesperforating a vertebra with at least a first hole, supporting aperforation guide with a guide support, guiding a perforation tool withthe perforation guide, and perforating the vertebra with a second hole(or shaped cavity) aligned by the perforation guide. The first hole canbe shaped to receive a prosthetic fixation element. The guide supportcan be positioned by a portion of the vertebra defining a hole. Thesecond hole can be shaped to receive a first prosthetic anti-rotationelement.

In some embodiments, the method can include the step of using theperforation tool while at least partly removing the guide support.

Various embodiments include the step of perforating the vertebra with athird hole aligned by the perforation guide. The third hole can beshaped to receive a second prosthetic anti-rotation element.

In some embodiments, the method can include the step of using theperforation tool while least partly removing the guide support.

The guide support can be inserted while perforating the vertebra withthe first hole. The guide support can be inserted after perforating thevertebra with the first hole.

In yet another aspect, a vertebral prosthesis tool includes a guidesupport and a perforation guide.

The guide support can be stabilized by a first hole of the vertebra. Thefirst hole can be shaped to receive a prosthetic fixation element of thevertebral prosthesis. The vertebral prosthesis can form a facet jointwith a second vertebral prosthesis.

The perforation guide can be coupled to the guide support. Theperforation guide can guide a perforation tool to perforate the vertebrawith a second hole aligned by the perforation guide. The second hole canbe shaped to receive a prosthetic anti-rotation element of the vertebralprosthesis.

Other features and advantages of the invention are set forth in thefollowing description and drawings, as well as in the appended claims.

In some embodiments, a system for vertebral implantation comprises afirst vertebral prosthesis comprising a first fixation element adaptedto be inserted into a first hole formed in a vertebra, the firstfixation element having a first longitudinal axis; a second vertebralprosthesis comprising a second fixation element adapted to be insertedinto a second hole formed in the vertebra, the second fixation elementhaving a second longitudinal axis; and a cross-bar connecting the firstvertebral prosthesis and the second vertebral prosthesis; wherein thefirst vertebral prosthesis comprises an anti-rotational elementextending along the first fixation element of the first vertebralprosthesis, wherein the anti-rotational element is configured to resista rotational force that would cause rotation of the first fixationelement in the first hole of the vertebra.

In other embodiments, a system for vertebral implantation comprises afirst vertebral prosthesis comprising a first proximal shaft having alongitudinal axis and a first distal shaft having a longitudinal axisthat differs from the longitudinal axis of the proximal shaft, whereinthe first distal shaft is configured to be inserted into a first holeformed in a vertebra; a second vertebral prosthesis comprising a secondproximal shaft and a second distal shaft, wherein the second distalshaft is configured to be inserted into a second hole formed in thevertebra; and a cross-bar connecting the first vertebral prosthesis andthe second vertebral prosthesis; wherein the first vertebral prosthesiscomprises one or more anti-rotational elements extending along the firstdistal shaft of the first vertebral prosthesis, wherein the one or moreanti-rotational elements are configured to resist a rotational forcethat would cause rotation of the first distal shaft in the first hole ofthe vertebra.

In other embodiments, a system for vertebral implantation comprises afirst vertebral prosthesis comprising a first proximal shaft having alongitudinal axis and a first distal shaft having a longitudinal axisthat differs from the longitudinal axis of the proximal shaft, whereinthe first proximal shaft transitions into the first distal shaft via abend; a second vertebral prosthesis comprising a second proximal shaftand a second distal shaft, wherein the second proximal shaft transitionsinto the second distal shaft via a bend; and a cross-bar connecting thefirst vertebral prosthesis and the second vertebral prosthesis; whereinthe first vertebral prosthesis comprises one or more anti-rotationalelements extending along a length of the first vertebral prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral elevation view of a normal human spinal column;

FIG. 2 is a superior plan view of a normal human lumbar vertebra;

FIG. 3 is a lateral elevation view of adjoining normal human lumbarvertebrae L4 and L5;

FIG. 4 is a perspective view of a cephalad prosthesis for replacing theinferior half of a natural facet joint on a superior vertebral body;

FIGS. 5A and 5B provide a perspective and proximal sectional view,respectively, of a vertebral prosthesis portion with blades;

FIGS. 6A, 6B, and 6C provide a side elevation view, another sideelevation view, and a perspective view, respectively, of a vertebralprosthesis portion with a paddle;

FIGS. 7A, 7B, 7C, and 7D provide a side elevation view, plan view,distal sectional view, and perspective view, respectively, of avertebral prosthesis portion with a fixation element having a bend and apaddle;

FIGS. 8A, 8B, and 8C provide a side elevation view, plan view, andperspective view, respectively, of a vertebral prosthesis portion with afixation element having a bend, a paddle, and additional distallylocated anti-rotation elements;

FIGS. 9A and 9B provide a perspective views of a vertebral prosthesisportion with a paddle, straight fixation element, and additionalanti-rotation elements;

FIGS. 10A and 10B provide a perspective view and a distal end view,respectively, of a vertebral prosthesis portion with an intersection ofmultiple projections;

FIGS. 11A, 11B, 11C, and 11D provide a side view, a perspective view,another side view, and a distal end view, respectively, of a vertebralprosthesis portion with a helical projection;

FIGS. 12A and 12B provide a perspective view and a distal end view,respectively, of a vertebral prosthesis portion with two helicalprojections;

FIGS. 13A and 13B provide a perspective view and a distal end view,respectively, of a vertebral prosthesis portion with longitudinaldepressions;

FIGS. 14A and 14B provide a perspective view and a distal end view,respectively, of a vertebral prosthesis portion with helicallongitudinal depressions and a fixation element with a bend;

FIG. 14C provides a perspective view of a pair of vertebral prosthesis,as in FIGS. 14A and 14B, connected by a cross-bar member;

FIGS. 15A, 15B, 15C, and 15D provide, a side view, an isometric view anda distal end view, a sectional view taken along the line shown in thedistal end view FIG. 15C respectively, of a vertebral prosthesis portionwith tapered longitudinal depressions and perimeter depressions;

FIGS. 16A and 16B provides a perspective view of a vertebral prosthesisportion with separated members;

FIGS. 17A, 17B, and 17C provide a perspective view, a side view, and adistal end view, respectively, of a vertebral prosthesis portion withwings;

FIGS. 18A through 18F illustrate different steps in a vertebralprosthesis method for the vertebral prosthesis of FIGS. 17A through 17C;

FIG. 19 is a close up view of the vertebral prosthesis tool used in themethod of FIGS. 18A through 18F;

FIGS. 20A and 20B show a perspective view and a close-up view,respectively, of a vertebral prosthesis tool for a vertebral prosthesiswith proximal anti-rotation features;

FIGS. 21A and 21B show a vertebral prosthesis portion with proximalprojections, and the insertion of the prosthesis portion into a vertebrafollowing the vertebral prosthesis tool of FIGS. 20A and 20B,respectively;

FIG. 22 is a perspective view of an installed vertebral prosthesisaccording to an embodiment of the invention where a fixation element isinserted into anti-rotation element;

FIG. 23 is a perspective view of an installed vertebral prosthesisaccording to another embodiment of the invention where a fixationelement is inserted into anti-rotation element; and

FIG. 24 is a perspective view of a vertebral prosthesis portion shapedto resist rotational force.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure presented herein provides details to enablethose skilled in the art to practice various embodiments of theinvention, the physical embodiments disclosed herein merely exemplifythe invention, which may be embodied in other specific structure.Accordingly, while preferred embodiments of the invention are describedbelow, details of the preferred embodiments may be altered withoutdeparting from the invention. All embodiments that fall within themeaning and scope of the appended claims, and equivalents thereto, areintended to be embraced by the claims.

Embodiments of the present invention may be used, with advantage, on awide variety of prosthesis devices, particularly spinal prostheses. Someof these prostheses, systems, and methods are discussed in the followingapplications entitled: “Facet Arthroplasty Devices And Methods”, by MarkA. Reiley, Ser. No. 09/693,272, filed Oct. 20, 2000, now U.S. Pat. No.6,610,091, issued Aug. 26, 2003; “Prostheses, Tools And Methods ForReplacement Of Natural Facet Joints With Artificial Facet Joint”, byLawrence Jones et al., Ser. No. 10/438,295, filed May 14, 2003;“Prostheses, Tools And Methods for Replacement Of Natural Facet JointsWith Artificial Facet Joint”, by Lawrence Jones et al., Ser. No.10/438,294, filed May 14, 2003; “Prostheses, Tools And Methods ForReplacement Of Natural Facet Joints With Artificial Facet Joint”, byLawrence Jones et al., Ser. No. 10/615,417, filed Jul. 8, 2003;“Prosthesis For the Replacement of a Posterior Element of a Vertebrae”,by T. Wade Fallin et al., U.S. Pat. No. 6,419,703; “Multiple Facet JointReplacement”, by E. Marlowe Goble et al., U.S. Pat. No. 6,565,605;“Facet Joint Replacement”; by E. Marlowe Goble et al., U.S. Pat. No.6,579,319; “Method and Apparatus for Spine Joint Replacement”; by E.Marlowe Goble et al., Ser. No. 10/090,293, filed Mar. 4, 2002; and“Polyaxial Adjustment Of Facet Joint Prostheses, by “Mark A. Reiley etal., Ser. No. 10/737,705, filed Dec. 15, 2003, all of which are herebyincorporated by reference for all purposes.

FIGS. 5A and 5B show one embodiment of a vertebral prosthesis portion500 with proximally positioned blades 504 that function as anti-rotationelements. The vertebral prosthesis portion 500 has a proximal portion502 with a pair of blades 504. The two blades 504 are positioned onopposite sides of the perimeter of the vertebral prosthesis portion 500,and are thus positioned apart by about 180 degrees. Also shown is agrooved portion 505 having grooves 506 along the periphery of thevertebral prosthesis portion 500. The illustrated grooved portion 505has grooves 506 that taper in a proximal direction along the vertebralprosthesis portion 500. Other groove configurations as possible, forexample, see FIGS. 6A, 6B, 6C, and 9A and 9B discussed in further detailbelow. Additionally, there may be embodiments having no grooves. In theillustrated embodiment, a transition section 525 separates the proximalportion 502 from the grooved portion 505. While the illustratedtransition section 525 has a uniform, linear transition from thediameter of the proximal portion 502 to the grooved portion 505, othertransition sections are possible depending upon the relative geometry ofthe grooved portion 505 and the proximal portion 502. In one embodiment,the transition section 525 can serve as a cement restrictor, preventingand/or inhibiting cement flow out of the vertebral body. In someembodiments, a transition section 525 may not be used.

Alternative embodiments of the vertebral prosthesis portion 500 may haveone blade, three blades, or more blades. Alternative embodiments canalso employ a different amount of spacing other than 180 degrees betweenmultiple blades for embodiments with multiple blades, and the spacingcan be the same or different between the multiple blades. While theembodiment illustrated in FIGS. 5A and 5B illustrates blades 504separated by convex portions 520, other configurations are possible. Forexample, the blades 504 may be separated by concave sections asillustrated, for example, in FIG. 15D or in combinations of convex andconcave portions. Although the illustrated blades 504 have pointedtriangular profiles, alternative embodiments can have rounded points, nopoints, and/or other profiles of other geometries, such as square,rectangular, trapezoidal, arcuate, etc and combinations thereof. Inaddition, blades 504 have a uniform incline section 514 and declinesection 516 and a single height ridge 518. Other configurations arepossible. For example, the incline and decline sections 514, 516 may bedifferent as in, for example, FIGS. 17A, 17B and 17C. In one embodiment,the blades 504 are sufficiently small such that the blades 504 can fitinto the same vertebral hole that receives the fixation element. It isto be appreciated that embodiments of the proximal anti-rotationelements of vertebral prosthesis portion 500 may be used in combinationwith other vertebral prosthesis portions described below. In addition,the advantages of the proximal anti-rotation features of vertebralprosthesis portion 500 may be combined with conventional prosthesisfasteners resulting in a hybrid prosthesis fastener having aconventional distal portion and a proximal portion having anti-rotationsfeature or features of the vertebral prosthesis portion 500.

FIGS. 6A, 6B, and 6C show an embodiment of a vertebral prosthesisportion 600 with a paddle 604 and grooves as an anti-rotation element.While desiring not to be bound by theory, it is believed that the widesurface area(s) provided by the anti-rotational paddle embodiments ofthe present invention provide greater resistance to the torque loadsapplied to the prosthesis and attempted rotation of the paddle withinthe vertebra. For example, the additional of surface projections and/orpits can significantly increase the total surface are of the prosthesis,thereby increasing the ability of any adhesion between the prosthesisand the surrounding material (such as bone cement, epoxy or in-growingbony material) to secure the prosthesis in position. As another example,the additional of surface projections and pits can interact with thesurrounding material to create a geometric or mechanical “interlock”that resists relative motion between the prosthesis and the surroundingmaterial. As such, the paddle embodiments of the present inventiondescribed herein act as improved anti-rotational elements. Similarly,other anti-rotation elements described herein are also used tocounteract the torque loads developed within and acting upon variousportions of vertebral prosthesis.

The vertebral prosthesis portion 600 has a distal end 601 and a proximalend 602. The proximal end 602 is configured to accept tooling andinstruments to secure the vertebral prosthesis portion 600 into thevertebra and/or to provide an attachment point to another vertebralprosthesis component. A distal portion of a fixation element has apaddle 604 configured to act as an anti-rotation element to prevent therotation of the vertebral prosthesis portion 600 once implanted into avertebra. Alternative embodiments of the vertebral prosthesis portion600 can have multiple paddles. Although the illustrated paddle 604 has arounded profile, alternative embodiments may have different profilesincluding, for example, one or more corners. Although the illustratedpaddle 604 is flat, alternative embodiments can have nonflat contours,with one or more concave and/or convex features.

FIGS. 6A, 6B, and 6C also illustrate an embodiment of an anti-pull outfeature of the vertebral prosthesis portion 600. Embodiments of thevertebral prosthesis portion 600 also include anti-pull out features. Asused herein, an anti-pull out feature refers to an element orcombination of elements of a prosthesis portion or fastener acting tomitigate, minimize or counteract forces bearing upon the prosthesisportion or fastener to disengage, loosen, advance, pull or otherwiseaxially translate the fastener relative to a desired position on orwithin the vertebra. (For purposes of this disclosure, anti-pulloutforces can be interpreted to include, but are not limited to, both“pull” and “push” forces which serve to translate the prosthesis along alongitudinal axis outward or inward relative to the targeted vertebralbody.) In the illustrated embodiment, the vertebral prosthesis portion600 includes a proximal grooved portion 605 having proximal grooves 606and a distal grooved portion 615 having distal grooves 617. In theillustrated embodiment, proximal grooves 606 have a proximal tip with awidth that increases distally and distal grooves 617 have a nearlyconstant width terminating in a distal tip. A reduced diameter portion608 separates the proximal grooved portion 605 from the distal groovedportion 615. The proximal grooves 606, distal grooves 617 and reduceddiameter section 608 act to increase the surface area of the vertebralprosthesis portion 600. By increasing the surface area of the vertebralprosthesis portion 600 provides greater attachment between the vertebralprosthesis portion 600 and the vertebra. The greater amount of surfacearea may be used advantageously with bone cement, bone growth compoundsor other materials used to bond the external surfaces the vertebralprosthesis portion 600 to the interior of the vertebra. The greatersurface area allows, in embodiments where bone fixation cement is used,more cement to be present along the length and a particularly greateramount of cement or fixation material to be present about the reduceddiameter section 608. The increased amount of cement present adjacentthe reduced diameter portion 608 produces a section of increaseddiameter that counteracts pull out forces. Other configurations,arrangements and geometries of the proximal grooved portion 605, reduceddiameter portion 608, and distal grooved portion 615 are possible. Forexample, different groove configurations are possible (e.g., FIGS. 9A,13A and 15F), there may be multiple distal or proximate grooved portions(e.g., FIG. 15B), multiple reduced diameter portions (e.g., FIG. 15B) ordifferent paddle configurations (e.g., FIGS. 7A-7D and FIGS. 8A-8C).

FIGS. 7A, 7B, 7C, and 7D show an embodiment of a vertebral prosthesisportion 700 with a fixation element having a bend 710, and a paddle 704as an anti-rotation element, similar to the vertebral prosthesis portionshown in FIGS. 6A, 6B, and 6C. The vertebral prosthesis portion 700includes a distal end 701 and a proximal end 703. The proximal end 703includes a bearing element 715 for engagement to other portions of thevertebral prosthesis. To accommodate a number of different facet jointprosthesis configurations, the fixation element includes a bend 710connected to a shaft 735 having a paddle 704 attached thereto.

The vertebral prosthesis portion 700 also illustrates an embodiment of amodular prosthesis fastener concept. For example, in some embodiments,the shaft 735 is detachably fastened to the attachment point 740. Theshaft 735 has a length “1” between the attachment point 740 and theproximate end of the paddle 704. The shaft 735 is detachably coupled tothe attachment point 740 to allow for shafts 735 of different lengths tobe used with different configurations of the vertebral prosthesisportion 700 thereby providing a modular vertebral prosthesis. As such,in use, the shaft 735 may be detached from the attachment point 740 andreplaced with a shaft 735 having a different length “1” as needed untilthe proper alignment of the vertebral prosthesis is achieved. Modularcomponents can be attached to the prosthesis using one or moreattachments methods well known in the art, including threaded screws,morse tapers, adhesives or set screws.

While the modular concept has been described with regard to thevertebral prosthesis 700, it is to be appreciated that other embodimentsof the vertebral prosthesis portions described herein may have a portionor portions that are detachably coupled in furtherance of the modularvertebral prosthesis concept. For an alternative example, the shaft 735may be of fixed length and permanently attached to the attachment point740 while the detachable attachment point is positioned between theshaft 735 and the paddle 704 thereby allowing paddles 704 of differentlengths to be used. In yet another alternative, both the shaft and thepaddle may have detachable attachment points thereby allowing variousshaft lengths and configurations and paddle lengths and configurationsto be used in furtherance of the modular vertebral prosthesis conceptsdescribed herein. It is to be appreciated that the detachable attachmentpoint may be positioned between any portion or portions of theembodiments of the vertebral prosthesis portions described herein andelsewhere in this patent application.

In an alternate embodiment, one or more sections of the vertebralprosthesis may be made of a deformable or shape-memory material (such asNitinol or similar materials), which permits the physician to makeadjustments to the prosthesis geometry to “form-fit” the implant to thepatient's specific anatomy. In the case of Nitinol, the material can beheated or cooled away from the body temperature (depending upon the typeof material and it's martensitic/austenitic properties), be deformed toa desired shaped, and then held in the deformed position and allowed toreturn to the body temperature, thereby “hardening” into the desiredshape or form. Such an embodiment would facilitate a reduction in thenumber of sections or “modules” required for a modular prosthesis, aseach module could assume a variety of desired positions.

While the angle of the illustrated bend 710 is acute, other embodimentsof the vertebral prosthesis portion 700 can have bend 710 having a rightangle or an obtuse angle. Alternative embodiments of the vertebralprosthesis portion 700 may include two, three, or more bends 710. In theillustrated embodiment, the paddle 704 has a flat surface 720 and aproximal end having a transition portion 730. The flat surface 720 isillustrated in the same plane in which the fixation element has the bend710. In other embodiments, the paddle 704 has a flat surface 720 inanother plane, and/or a nonflat contour, with one or more concave and/orconvex features or have paddle shapes similar to the distal portionsillustrated in FIGS. 10A, 101B, 13A and 13B. The transition portion 730has a width that decreases linearly in a proximal direction. Otherconfigurations of the transition portion 730 are possible fortransitioning from the paddle 704 to the shaft 735 of the vertebralprosthesis portion 700. The alternative shapes of the transition portioninclude, for example, a non-linear decreasing proximal width, asymmetricportions, curved portions or compound portions.

FIGS. 8A, 8B, and 8C show an embodiment of a vertebral prosthesisportion 800 with a fixation element having a bend 810, and compoundanti-rotational elements included in the paddle 804. A proximal socketelement 807 is attached to the bend 810 by a proximal shaft 850. Adistal shaft 860 couples the bend 810 to the paddle 804. While theillustrated bend 810 has only a single, acute angle, it is to beappreciated that in other embodiments the bend 810 may have a have aright angle or an obtuse angle and may include two, three, or morebends. Further to the modular and configurable vertebral prosthesisconcepts described herein, one or more detachable connections may existbetween the various elements of the vertebral prosthesis portion 800. Inaddition, elements of different lengths (e.g., shafts 850, 860), size(e.g., socket 807 and paddle 804) or angular orientation (e.g., bend810, paddle 804) may be advantageously employed in furtherance of themodular vertebral prosthesis concept.

Embodiments of the vertebral prosthesis portion 800 may have paddle 804embodiments similar to the paddle embodiments shown and described withregard to vertebral prosthesis portion 700 (see e.g., FIGS. 7A, 7B, 7C,and 7D). The paddle 804 may include a flat face similar to face 720described above, however, other configurations are possible. Asillustrated, paddle 804 has a non-flat face 820 that may be convex,concave or have portions that are combinations of convex, concave orflat. Alternatively, the paddle surface 820 may be a flat surface inanother plane, and/or a nonflat contour, with one or more concave and/orconvex features. As illustrated, the paddle surface 820 is in the sameplane in as the bend 810. In other embodiments, the paddle surface(s)820 may not be in plane with the bend 810.

In addition to having paddle surfaces 820 of varying shape than earlierdescribed paddle embodiments, embodiments of the paddle 804 also includecompound or more than one anti-rotation elements. As discussed above,the paddle surfaces generally provide an anti-rotation orrotation-resistant component to the vertebral prosthesis. Additionally,embodiments of paddle 804 include other anti-rotational elements such asthe enlarged distal tip 812 having grooves 815 and projections 819. Theenlarged distal tip 812 may have one or more grooves 815 positioneddistally from the paddle 804. In some embodiments, the grooves occur inthe same plane as the plane of the paddle 804. In other embodiments,grooves can occur in multiple planes and/or planes that are differentfrom the plane of the paddle 804. Similarly, the distal tip may haveprojections 819 in the same or different plane with the faces of paddle804. While the illustrated projections 819 appear identical in shape andsize and are arranged parallel to the axis of the proximal shaft 860, itis to be appreciated that the projections 819 may have differentconfigurations. The projections 819 may not all be the same size or havethe same overall shape, have an asymmetrical orientation relative to thepaddle 804 or be positioned in a non-parallel arrangement with regard tothe axis of the proximal shaft 860.

FIGS. 9A and 9B illustrate an alternative embodiment of a vertebralprosthesis portion having anti-rotation and anti-pullout elements. Thepaddle 955 and proximal ridges 925, 927 act as anti-rotation elements.The reduced diameter section 940, grooved sections 930, 945 and reducedshank diameter 920, 922 act as anti-pullout elements. The vertebralprosthesis portions 900 and 990 are similar in many regards to vertebralprosthesis portion 600 if FIGS. 6A, 6B and 6C. However, severaldifferences are important. Paddle 955 has a flat face 960 but a rounded,tapered distal end 965 instead of a flat distal edge found on paddle 604(see FIG. 6B). Proximal grooves 935 have a constant width instead of atapered width (see FIG. 6A grooves 606). Distal grooves 950 have auniform width and a rounded distal end instead of a distal tip (grooves617 of FIG. 6B).

One notable difference between the prosthesis portions 900, 990 and theprosthesis portion 600 is the addition of the proximal anti-rotationsections 920, 922. The proximal anti-rotation sections 920, 922 includea shank having a diameter less than the shank 915 and a plurality (twoin the illustrated embodiments) of ridges that act as proximalanti-rotation elements. Vertebral prosthesis portion 900 has a proximalanti-rotation portion 920 and ridges 925 having an overall height h₁.Vertebral prosthesis portion 990 has a proximal anti-rotation portion922 and ridges 927 having an overall height h₂ These embodimentsadvantageously provide reduced shank sizes thereby allowing forincreased cement mantle (if cement is desired), while still providing amechanical “interlock” with the surrounding tissue that resistsprosthesis rotation (In various embodiments, the ridges can desirablyengage surrounding cortical bone at the pedicle entry point, which isoften stronger than the cancellous bone contained within the vertebralbody, although the ridges' engagement with either or both types of bonewill serve to resist rotation to varying degrees). In a specificembodiment of the prosthesis portion 900 the height h₁ is 8.25 mm andthe proximal anti-rotation section diameter is 6.5 mm but stillmaintains a moment of inertia (I_(y)) equal to that of a 7 mm rod. In aspecific embodiment if the prosthesis portion 990, the overall ridgeheight h₂ is 8.75 mm and the proximal anti-rotation section diameter is6.0 mm but the embodiment still maintains a moment of inertia (I_(y))equal to that of a 7 mm rod.

It is to be appreciated that the vertebral prosthesis portions 900 and990 may differ from the illustrated embodiments. For example, there maybe one or more ridges present in the proximal anti-rotation sections (asopposed to the pair of ridges disclosed above). The additional ridgesneed not have uniform cross sections or be uniformly spaced about theperimeter of the proximal anti-rotation section. The paddle face 960 mayhave a different face such as convex, concave or other compound shape orcombinations thereof.

FIGS. 10A and 101B show an embodiment of a vertebral prosthesis portion1000 with an intersection of multiple projections as an anti-rotationelement. The distal portion of the fixation element has threeprojections 1018. The three projections 1018 meet at an intersection1020 of the projections. The three projections 1018 meet at the center,as viewed from the distal end. In alternative embodiments multipleprojections can meet at an off-center position as viewed from the distalend. The three projections 1018 are positioned equidistantly about theperimeter of the fixation element, and are thus positioned apart byabout 120 degrees. Alternative embodiments can have one projection, twoprojections, four projections, or more projections. Alternativeembodiments can also employ a different amount of spacing other than 120degrees between multiple projections, and the spacing can be the same ordifferent between the multiple projections. Although the illustratedprojections 1018 have a trapezoidal profile as viewed from the side ofthe prosthesis portion, alternative embodiments can have other profilesof other geometries, such as square, rectangular, triangular, etc.

FIGS. 11A, 11B, 11C and 11D illustrate another embodiment of a vertebraeprosthesis portion having a helical projection that acts as ananti-rotation element. FIGS. 11A, 11B are right and left side views of avertebral prosthesis portion 1100. The vertebral prosthesis portion 1100has a distal tip 1105 and a proximal fitting 1110. The proximal fitting1110 is attached to a shank 1115 and a tapered shaft 1120. A single steptransition section 1130 is used to change diameters from the shank 1115to the proximal end of the tapered shaft 1120. A rounded profile ridge1122 spirals proximally from the distal tip 1105 to the transitionsection 1130. While the illustrated embodiment shows the ridge 1122beginning at the distant tip 1105 and spiraling continuously to thetransition section 1130, other configurations are possible where, forexample, the ridge begins at a position proximate to the distal tip 1105or ends distal to the transition section 1130. Moreover, the ridge 1122need not be continuous but may be segmented into a plurality of sectionshave the same or different lengths. (If desired, the interrupted ridgecould additionally act as a “self-locking” feature to resist undesiredremoval of the prosthesis.) The ridge 1122 need not be of uniform heightbut may have various heights that increase or decrease in a proximaldirection or alternate such as in a sinusoidal pattern. FIG. 11Cillustrates a view of the vertebral prosthesis 1100 viewed proximallyfrom the distal tip 1105. The ridge 1122 has a pitch of about onerevolution meaning that as the ridge 1122 spirals along the taperedshaft 1120 it traces a path that traverses a single rotation absent thetapered shaft. In alternative embodiments, the ridge 1122 may traversethe tapered shaft 1122 at an increased pitch (more than one revolution)or a decreased pitch (less than one revolution, see e.g. FIG. 11D). Inaddition to changing the pitch, the ridge 1122 may have othercross-sectioned shapes other than rounded such as, for example, a sharpedge or triangular cross section as in FIG. 1D.

Vertebral prosthesis portion 1150 illustrates and alternative embodimentof the helical ridge anti-rotation element (FIG. 1I D). Vertebralprosthesis portion 1150 is similar in many respects to vertebralprosthesis portion 1100 and similar reference numbers have been used forlike components. Vertebral prosthesis portion 1150 has a multiple steptransition section 1155 between the shank 1115 and the tapered shaft1160. The tapered shaft 1160 has a more gradual taper than the taper intapered shaft 1120. The ridge 1170 has a sharp edge and a pitch of lessthan one revolution. Desirably, the transition in the shaft will reduceand/or eliminate the stress concentration or “stress riser” inherent inthe diameter transition.

In an alternative embodiment to the single ridge anti-rotation element(FIGS. 11A-11D), a vertebral prosthesis portion 1200 may have more thanone ridge anti-rotation element (FIGS. 12A, 12B). The vertebralprosthesis portion 1200 has a distal tip 1205 and a proximal end 1210. Ashank 1215 is attached to the proximal end 1210 and a stepped transitionsection 1255. A tapered shaft 1260 extends from the stepped transitionsection 1255 to the distal tip 1205. Two ridges 1222, 1224 projectoutwardly from the tapered shaft 1260. Using the orientation at thedistal tip 1205 (FIG. 12B), the upper ridge 1222 has a rounded topsurface and is wider than the lower ridge 1224 that is narrower with amore pronounced or sharper ridge top surface. In the illustratedembodiment, ridges 1222, 1224 have the same pitch of less than onerevolution. It is to be appreciated that the ridges 1222, 1224 couldhave a pitch greater than one or each ridge could have a different pitchor more than two ridges could traverse tapered shaft 1260. Otheralternative ridge configurations as described above with regard toridges 1122 and 1170 (e.g., FIGS. 11A, 11D) are applicable to ridges1222, 1224. The ridges 1222, 1224 project from opposite sides of thetapered shaft 1260 and are evenly spaced apart by a separation angle ofabout 180 degrees. Alternative embodiments can have three ridge orhelical projections, four helical projections, or more helicalprojections. Alternative embodiments and the illustrated embodiment mayalso employ a separation angle or angles of other than 180 degreesbetween helical projections and the spacing can be uniform between allprojections or be variable and/or different between projections. Asdescribed above, the ridges or helical projections may begin at alocation on the tapered shaft 1260 proximal to the distal tip 1205 andmay end distal to the stepped transition section 1255.

FIGS. 13A and 13B illustrate an embodiment of a vertebral prosthesisportion 1300 have longitudinal grooves as anti-rotation elements. Thevertebral prosthesis portion 1300 has a distal end 1305 and a proximateend 1310 attached to a shank 1320. A transition section 1325 separatesthe shank 1320 from the proximal grooved section 1330 having grooves1335 formed therein. A reduced diameter section 1340 separates theproximal grooved section 1330 from the distal grooved section 1345. Thedistal grooved section 1345 has grooves 1350 formed therein. As can beseen more clearly in distal end view of FIG. 13B, there are four grooves1350 in the illustrated embodiment. The groove configuration ofvertebral prosthesis portion 1300 differs from earlier described grooves506 (FIG. 5A), grooves 945, grooves 935 (FIG. 9A, 9B) in a number ofways. The grooves 1350 are much wider and there are fewer of them thanin previous embodiments. The grooves 1350 are wider distally and taperproximally to the reduced diameter section 1340. The grooves 1350 areevenly spaced about the distal grooved section 1345 and have the samerounded cross section (see FIG. 13B). However, in alternativeembodiments, the grooves 1350 have different spacings and differentcross-sectioned shapes.

It is to be appreciated that each of the longitudinal grooves ordepressions 1350 has a longitudinally varying profile, narrowing as thegroove extends proximally. In alternative embodiments, thelongitudinally varying profile can widen or remain constant as thelongitudinal depression or groove extends proximally (if desired, theycan change in depth as they narrow in width). Although in theillustrated embodiment, all of the longitudinal depressions or grooves1350 are identical, in other embodiments, the multiple longitudinaldepressions can differ, for example by having different profiles,lengths, starting and/or ending points, etc. Alternative embodiments canhave one longitudinal depression, two longitudinal depressions, threelongitudinal depressions, five longitudinal depressions, or morelongitudinal depressions. Alternative embodiments can also employ adifferent amount of spacing other than 90 degrees between multiplelongitudinal depressions for embodiments with multiple longitudinaldepressions, and the spacing can be the same or different between thelongitudinal depressions.

The proximal grooved section 1330 has fewer grooves 1335 than previouslydescribed proximal grooved sections (e.g. FIGS. 5A, 9A and 9B). Thereare two grooves 1335 in the proximal grooved section 1330, although onlyone is visible in FIG. 13A. Grooves 1335 align with a distal groove 1350in the illustrated embodiment. The grooves 1335 have a groove profilethat is wider distally and tapering proximally to a tip at transitionsection 1325. It is to be appreciated that alternative embodiments mayhave one or more grooves 1335 to align one for one with grooves 1350. Inanother alternative embodiment, there may be the same number of grooves1335 as grooves 1350 however, grooves 1335 may be offset radically so asnot to align axially with grooves 1350 as illustrated. Both grooves1350, 1335 need not be parallel to the longitudinal axis if thevertebral prosthesis portion 1300 but may instead be arranged innon-parallel configurations with respect to the longitudinal axis of thevertebral prosthesis portion 1300.

FIGS. 14A and 14B show an embodiment of a vertebral prosthesis portion1400 with helical longitudinal depressions as anti-rotation elements anda fixation element with a bend. The illustrated embodiment of thevertebral prosthesis portion 1400 has a distal tip 1404 and a proximalend 1402. The proximal end 1402 includes a socket element 1407 forfurther attachment to a vertebral prosthesis. (Alternatively, theelement 1407 could comprise a bearing surface for slidably engaging acorresponding bearing surface (not shown) of a caudal portion of avertebral prosthesis). Proximal shaft 1415 is attached to the socketelement 1407 and the bend 1410. The tapered section 1430 transitionsfrom the proximal shaft 1415 to the distal shaft 1417 [as the proximalshaft 1415 is a different diameter than the distal shaft 1417.] Othertransitions are possible such as a stepped transition (e.g. section 740of FIG. 7B) or no transition if the diameter of the shafts 1415 and 1417are the same.

The distal shaft 1417 includes a plurality of longitudinal depressions1423 extending from the distal end 1404 to a point beyond the taperedsection 1430. The proximal end of the longitudinal depressions 1423 hasa bulbed section 1460. The distal shaft 1417 also includes a reduceddiameter section 1440. The reduced diameter section 1440, longitudinalgrooves 1423 and bulbed section 1460 may be used to increase the surfacearea of the vertebral prosthesis portion 1440 that is, when implanted,within a vertebra of the spine. The increased surface area allows formore area to support the cement mantle for applications using cement or,bony ingrowth for applications using bone ingrowth. It is to beappreciated that the longitudinal grooves 1423 may also be varied asdescribed elsewhere with regard to other grooves and, for example, asdescribed with regard to FIGS. 13A, 13B, 6A, 6B, 6C and 5A. In addition,alternative embodiments of bend 1410 are possible as described withregard to FIGS. 7A-7D and 8A-8C.

It is to be appreciated that each of the longitudinal depressions 1423has a longitudinally varying profile, narrowing as the longitudinaldepression extends proximally. In alternative embodiments, thelongitudinally varying profile can widen or remain constant as thelongitudinal depression extends proximally. Although in the illustratedembodiment all of the longitudinal depressions are identical, in otherembodiments, the multiple longitudinal depressions can differ, forexample by having different profiles, lengths, starting and/or endingpoints, etc. Alternative embodiments can have one longitudinaldepression, two longitudinal depressions, four longitudinal depressions,five longitudinal depressions, or more longitudinal depressions.

FIG. 14C depicts an alternate embodiment of the vertebral prosthesis ofFIG. 14A, 14B in which a pair of prosthesis 1400 are connected by across-bar 1405. Cross-bar 1405 can be a cylindrical member fitting intoopenings 1409 in each of the shafts 1415 of the prosthesis 1400 (or canbe virtually any rigid or semi-rigid member secured between the twoprosthesis), and the cross-bar 1405 desirably reduces or preventsrotation of the prosthesis 1400 relative to each other. When both of theprosthesis are secured into a targeted vertebral body through thepedicles (not shown), any torsional loads experienced by an individualprosthesis 1400 will be transferred to the shaft 1415 of the opposingprosthesis by the cross-bar 1405, which will convert the torsional loadto a transverse load acting on the opposing prosthesis. Desirably, thenewly loaded prosthesis can resist this transverse force, therebymaintaining the entire structure in a desired position. In thisembodiment, the cross-bar therefore “shares” and redistributes thetorsional loading experienced by an individual prosthesis, significantlyreducing the tendency for an individual prosthesis to rotate.

FIGS. 15A-15D illustrate a vertebral prosthesis portion 1500 having aplurality of grooved portions and reduced diameter portions asanti-rotation elements and anti-pullout elements. The vertebralprosthesis portion 1500 includes a proximal end 1505 and a distal end1510. A shank 1515 is connected to the proximal end 1505. A diametertransition section 1520 is used to step down the diameter from the shank1515 to the distal grooved section. The transition section 1520desirably limits or eliminates potential stress concentrations or“risers” which can occur due to this geometry change. Moreover, thetransition section 1520 desirably will form a tight fit with the openingformed in the bone, sealing the opening (not shown) and facilitatingpressurization of cement or other supplemental fixation material withinthe bone without cement exiting the opening—thereby ensuring theprosthesis is well-anchored in the fixation material, if used. Thevertebrae prosthesis portion 1500 includes three grooved sections: theproximal grooved section 1525 having proximal grooves 1530, the middlegrooved section 1540 having middle grooves 1545 and the distal groovedsection having distal grooves 1560. Additionally, there is provided aproximal reduced diameter section 1535 between the proximal groovedsection 1525 and the middle grooved section 1540 and a distal reduceddiameter section 1550 between the middle grooved section 1540 and thedistal grooved section 1555.

In the illustrated embodiment, the grooves 1530, 1545 and 1560 are ofsimilar size, shape and orientation. The grooves have a rounded crosssection profile best seen in FIG. 15D and pronounced or sharp ridges1565 between adjacent grooves. In addition, middle grooves 1545 andproximal grooves 1530 have a tapered width that decreases proximally.Other groove and reduced diameter configurations, cross section profileand angular orientations are possible and are described above withregard to other grooves and reduced diameter portions in otherembodiments as well as described with regard to FIGS. 6A, 6B, 6C, 14A,14B, 13A, 13B, 9A and 9B.

FIGS. 16A and 16B show an embodiment of a vertebral prosthesis fixationelement 1600 having separable members 1625 that, when deployed as inFIG. 16B, act as anti-rotation and anti-pullout elements to compensatefor forces, including torque, applied to the fixation element 1600 whenused to secure intervertebral implants. The vertebral prosthesisfixation element 1600 has at least two configurations, stowed 1605 (FIG.16A) and deployed 1610 (FIG. 16B). Vertebral prosthesis fixation element1605 illustrates the separable members 1625 in a stowed configurationand vertebral prosthesis fixation element 1610 illustrates the separablemembers 1625 in a deployed configuration. The stowed configuration 1605simplifies the transportation of the vertebral prosthesis fixationelement 1600 to the implantation site by maintaining the separablemembers 1625 in close proximity thereby reducing the overall fixationelement size. Inside of the vertebral implantation site, the separablemembers 1625 are placed into a deployed configuration whereby theseparable member ridges 1635 are urged into contact with the surroundingvertebra. The ridges 1635 may be arranged in any orientation relative tothe separable member 1625. Advantageously, when the separable members1625 are urged into a deployed configuration 1610 and into contact withthe surrounding vertebra, the size, shape, and orientation of the ridges1635 along the separable members 1625 “dig into” or press against thesurrounding material and secure the vertebral prosthesis fixationelement 1600 into position. More importantly, the size, shape andorientation of the ridges 1635 provide anti-rotation and/or anti-pulloutstability to the vertebral prosthesis fixation element 1600.

In the illustrated embodiments, the distal portion of the vertebralprosthesis fixation element 1600 has four separable members 1625separated by the longitudinal hole 1626. The longitudinal hole 1626permits a filling member 1628 to be inserted from the proximal end ofthe vertebral prosthesis fixation element 1600, causing the separablemembers 1625 to spread apart into the deployed configuration (i.e.,vertebral prosthesis fixation element 1610) with deployed spacing 1640separating adjacent separable members 1625. The exterior surface of eachseparable member 1625 has a plurality of continuous ridges 1635.Continuous ridges are single ridges that extend along the surface of aseparable member from one spacing 1640 to the next adjacent spacing1640. It is to be appreciated that the ridges may be segmented ridgesmeaning more than one ridge between adjacent spacings 1640. The ridges1635 in the illustrated embodiment are all continuous and the ridges1635 on each separable member 1625 are similarly oriented relative tothe separable members. It is to be appreciated that other ridgeconfigurations are possible, such as for example, combinations ofcontinuous and segmented ridges on a single separable member, as well asdifferent ridge orientations on the same separable member or differentridge orientations on different separable members. In addition,alternative embodiments can have more or fewer ridges than theillustrated embodiment, or be at least partly smooth.

Additionally, other embodiments of the vertebral prosthesis fixationelement 1600 can have two, three, five, or more separable members 1625.The filling member can be a smooth peg as shown, or alternatively a bar,a wire, or any other shape that, upon insertion into the longitudinalhole 1626, causes the separable members 1625 to move from a stowedconfiguration 1605 to a deployed configuration 1610.

In one embodiment, a vertebral prosthesis fixation element 1600 is usedto secure a vertebral prosthesis implanted between two vertebrae toprovide restoration of movement between the vertebrae. Features of thevertebral prosthesis fixation element 1600, such as the shape, size andorientation of the ridges 1635, advantageously secure the implantedvertebral prosthesis while providing anti-rotation capability for thetorques generated within the implanted prosthesis and applied to thevertebral prosthesis fixation element 1600. In another embodiment, avertebral prosthesis fixation element 1600 is used to secure at least aportion of a vertebral prosthesis connecting two adjoining vertebrae torestore movement between the adjoining vertebrae. In this embodiment,when the separable members are in a deployed configuration, at least aportion of the ridges on at least one separable member engages thesurrounding vertebrae and counteracts the forces generated by relativemotion between the adjoined vertebrae, and/or the forces generatedbetween the vertebral prosthesis and the vertebrae attached to thevertebral prosthesis.

FIGS. 17A, 17B, and 17C show an embodiment of a vertebral prosthesisportion with wings as anti-rotation elements. The two wings 1730 arepositioned on opposite sides of the perimeter of the fixation element,and are thus positioned apart by about 180 degrees. Alternativeembodiments can have one wing, three wings, or more wings. Alternativeembodiments can also employ a different amount of spacing other than 180degrees between multiple wings for embodiments with multiple wings, andthe spacing can be the same or different between the multiple wings.Although the illustrated wings 1730 have pointed triangular profiles,alternative embodiments can have rounded points, no points, and/or otherprofiles of other geometries, such as square, rectangular, trapezoidal,etc. In one embodiment, the wings 1730 can be sufficiently large suchthat the blades 1730 could fit into laterally extending slots (notshown) extending outward from to the vertebral hole that receives thefixation element.

FIGS. 18A through 18F illustrate an embodiment of a vertebral prosthesisplacement method for the vertebral prosthesis of FIGS. 17A through 17C.In FIG. 18A, the vertebra 1832 is perforated with a perforation tool1831 to make a hole. The hole is large enough to receive a fixationelement of a vertebral prosthesis. Although a drill is shown as theperforation tool, other perforation tools can be used, such as an auger,a laser, a broach, etc. FIG. 18B shows guide supports 1834 and 1835 ofvarious lengths which can be chosen depending on the depth of the holemade by the perforation tool. The guide supports 1834 and 1835 are sizedlarge enough such that the vertebra hole stabilizes the particular guidesupport that is inserted into the vertebra hole. For example, guidesupports 1834 and 1835 can include increased-diameter sections 1830which optimize centering in the vertebra hole. In alternativeembodiments, the guide support and perforation tool can be the same,such that the perforation tool does not have to be removed afterperforating the vertebra and the perforation tool also can be used as aguide support. FIG. 18C shows the guide support 1834 inserted into thehole made by the perforation tool. A perforation guide 1836 and a handle1838 are attached to the guide support 1834. FIG. 18D shows aperforation tool 1831 guided by the perforation guide 1836. Guided bythe perforation guide 1836, the vertebra 1832 is perforated with anotherhole. The perforation stop 1839 on the perforation tool 1831 strikes theperforation guide 1836, thereby stopping the perforation and definingthe depth of that hole. FIG. 18E shows another perforation process aidedby the perforation guide 1836. FIG. 18F shows that as the assembly ofthe handle 1838, perforation guide 1836, and guide support 1834 isremoved from the vertebra, the perforation tool 1831 can be used toremove the remainder of bone from the vertebra. This can be repeated foreach of the holes.

FIG. 19 is a close up view of the embodiment of the vertebral prosthesistool used in the method of FIGS. 18A through 18F. Perforation guide 1936has an anti-rotation flat 1944 to ensure alignment of the perforationtools 1931. Locking hex nuts 1942 allow the physician to adjust thedepth of the perforation tools if necessary.

FIGS. 20A and 20B show an embodiment of a vertebral prosthesis tool forthe vertebral prosthesis with proximal projections as anti-rotationelements. Perforation guide 2036 is attached to guide support 2034. Inthis embodiment, the guide support 2034 includes a perforation tool2031. In alternative embodiments, the guide support and perforation toolcan be distinct, such that the perforation tool is removed afterperforating the vertebra, and replaced with a guide support.

FIG. 21A shows an embodiment of a vertebral prosthesis portion withproximal projections. In alternative embodiments, the projections can beblades and/or wings. Alternative embodiments can have one projection,three projections, or more projections. The two proximal projections2116 are positioned on opposite sides of the perimeter of the proximalportion of the fixation element, and are thus positioned apart by about180 degrees. Alternative embodiments can also employ a different amountof spacing other than 180 degrees between multiple proximal projectionsfor embodiments with multiple proximal projections, and the spacing canbe the same or different between the multiple proximal projections. FIG.21B shows the insertion of the prosthesis portion of FIG. 21A into avertebra following the use of the vertebral prosthesis tool of FIGS. 20Aand 20B.

FIG. 22 is a perspective view of an installed vertebral prosthesisaccording to an embodiment of the invention where a fixation element isinserted into an anti-rotation element. The anti-rotation element 2241defines a hole, into which the fixation element 2243, shown as a screw,is inserted into. Both the hole defined by the anti-rotation element2241 and the fixation element 2243 have a taper 2245, which can be aMorse taper, if desired. The anti-rotation element 2241 and the fixationelement 2243 can thereby couple together with an interference fit whenthe fixation element 2243 is inserted into the anti-rotation element2241. In various embodiments, the anti-rotation element can include abend, or be straight; and the first fixation element can be straight, orinclude a bend. The bend can be sharp or gradual. In alternativeembodiments, the first fixation element can define a hole into which theanti-rotation element is inserted.

FIG. 23 is a perspective view of an installed vertebral prosthesisaccording to another embodiment of the invention where a fixationelement is inserted into anti-rotation element, similar to theembodiment of FIG. 22. The fixation element 2343 is a stem. In otherembodiments, the fixation element and the anti-rotation element can be acorkscrew, wire, staple, adhesive, bone, and other materials known inthe prosthetic arts.

FIG. 24 is a perspective view of a vertebral prosthesis portion shapedto primarily resist rotational force. The shape of the fixation element2400 has a bend. Also shown is a longitudinal depression 2423 andproximal projections 2416. Alternative embodiments can have neither thelongitudinal depression 2423 nor the proximal projections 2416. Somealternative embodiments include limited anti-rotation elements, relyingprimarily on the non-uniform shape of the fixation element to resistrotation. Other embodiments can include anti-rotation elements otherthan longitudinal depressions and proximal projections.

For purposes of illustration and explanation of the anti-rotation and/oranti-pullout advantages of embodiments of the present invention,vertebral prosthesis portions have been illustrated and described inaxial shaft configurations (e.g., FIGS. 6A-6C, 9A-9B, 10A, 11A-13B) andcurved shaft configurations (e.g., 7A-8C, 14A-14B, and 22-24). It is tobe appreciated that the anti-rotation and anti-pull out embodimentsdescribed in each are not limited to only the illustrated and describedembodiments but are applicable to other different embodiments, as asubstitute to or combination with the described and illustratedembodiment. For clarity, the various embodiments of the invention havebeen referred to as portions of a vertebral prosthesis havinganti-rotation and/or anti-pull out elements. It is to be appreciatedthat while these elements provide the additional advantages describedherein, these elements are also fasteners that act generally to securethe various loading elements and components of the prosthesis to thespine.

While preferred embodiments of the invention have been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

1. A system for vertebral implantation, comprising: a first vertebralprosthesis comprising a first fixation element adapted to be insertedinto a first hole formed in a vertebra, the first fixation elementhaving a first longitudinal axis; a second vertebral prosthesiscomprising a second fixation element adapted to be inserted into asecond hole formed in the vertebra, the second fixation element having asecond longitudinal axis; and a cross-bar connecting the first vertebralprosthesis and the second vertebral prosthesis; wherein the firstvertebral prosthesis comprises an anti-rotational element extendingalong the first fixation element of the first vertebral prosthesis,wherein the anti-rotational element is configured to resist a rotationalforce that would cause rotation of the first fixation element in thefirst hole of the vertebra.
 2. The system of claim 1, wherein the firstfixation element comprises a tapered section.
 3. The system of claim 1,wherein the anti-rotational element comprises a longitudinal depression.4. The system of claim 3, wherein the longitudinal depression ishelical.
 5. The system of claim 1, wherein the first vertebralprosthesis further comprises a bearing surface.
 6. The system of claim1, wherein the first vertebral prosthesis comprises a socket element forattachment to a vertebral prosthesis.
 7. The system of claim 1, whereinthe cross-bar is inserted into openings in the first vertebralprosthesis and the second vertebral prosthesis.
 8. A system forvertebral implantation, comprising: a first vertebral prosthesiscomprising a first proximal shaft having a longitudinal axis and a firstdistal shaft having a longitudinal axis that differs from thelongitudinal axis of the proximal shaft, wherein the first distal shaftis configured to be inserted into a first hole formed in a vertebra; asecond vertebral prosthesis comprising a second proximal shaft and asecond distal shaft, wherein the second distal shaft is configured to beinserted into a second hole formed in the vertebra; and a cross-barconnecting the first vertebral prosthesis and the second vertebralprosthesis; wherein the first vertebral prosthesis comprises one or moreanti-rotational elements extending along the first distal shaft of thefirst vertebral prosthesis, wherein the one or more anti-rotationalelements are configured to resist a rotational force that would causerotation of the first distal shaft in the first hole of the vertebra. 9.The system of claim 8, wherein the first distal shaft of the firstvertebral prosthesis is tapered.
 10. The system of claim 8, wherein theanti-rotational elements comprise longitudinal depressions.
 11. Thesystem of claim 10, wherein the longitudinal depressions are helical.12. The system of claim 8, wherein the first proximal shaft has adifferent diameter from the first distal shaft of the first vertebralprosthesis.
 13. The system of claim 8, wherein the first proximal shafttransitions into the first distal shaft via a bend.
 14. The system ofclaim 8, wherein the proximal shaft includes a socket element.
 15. Asystem for vertebral implantation, comprising: a first vertebralprosthesis comprising a first proximal shaft having a longitudinal axisand a first distal shaft having a longitudinal axis that differs fromthe longitudinal axis of the proximal shaft, wherein the first proximalshaft transitions into the first distal shaft via a bend; a secondvertebral prosthesis comprising a second proximal shaft and a seconddistal shaft, wherein the second proximal shaft transitions into thesecond distal shaft via a bend; and a cross-bar connecting the firstvertebral prosthesis and the second vertebral prosthesis; wherein thefirst vertebral prosthesis comprises one or more anti-rotationalelements extending along a length of the first vertebral prosthesis. 16.The system of claim 15, wherein the anti-rotational elements comprisesdepressions.
 17. The system of claim 15, wherein the first proximalshaft has a different diameter from the first distal shaft.
 18. Thesystem of claim 15, wherein the first distal shaft is tapered andconfigured to fit into a first hole of a first vertebra.
 19. The systemof claim 15, wherein the first proximal shaft comprises a socketelement.
 20. The system of claim 15, wherein the first proximal shaftcomprises a bearing surface for slidably engaging a correspondingbearing surface of another prosthesis.